Touchscreen electrode arrangement

ABSTRACT

An assembly has an array of first electrodes distributed across an active area of the touchscreen assembly such that the density of first electrodes increases in a first direction across the touchscreen. An array of second electrodes is distributed across an active area of the touchscreen assembly such that the density of second electrodes decreases in the first direction across the touchscreen.

RELATED APPLICATION

This application is a continuation under 35 U.S.C. § 120 of U.S.application Ser. No. 12/606,934, filed Oct. 27, 2009 and entitled“Touchscreen Electrode Arrangement,” which is incorporated herein byreference.

BACKGROUND

Touchscreen displays are able to detect a person's touch within theactive or display area, such as detecting whether a finger is presentpressing a fixed-image touchscreen button or detecting the presence andposition of a finger on a larger touchscreen display. Some touchscreenscan also detect the presence of elements other than a finger, such as astylus used to generate a digital signature, select objects, or performother functions on a touchscreen display.

Touchscreens are often used as interfaces on electronic devices,appliances, and other such electronic systems because the display behindthe touchscreen can be easily adapted to provide instruction to the userand to receive various types of input, thereby providing an intuitiveinterface that requires very little user training to use effectively.Inexpensive and efficient touchscreen technologies enable incorporationof touchscreens into inexpensive commercial devices, but theseinexpensive technologies should also desirably be durable and haverelatively high immunity to noise, moisture or dirt, or other unintendedoperation to ensure reliability and longevity of the touchscreenassembly. These desirable attributes also largely apply to other inputdevices such as trackpads and pen entry tablets.

Use of a touchscreen as part of a display also allows an electronicdevice to change the display image, presenting different buttons,images, or other regions that can be selected, manipulated, or actuatedby touch. Touchscreens can therefore provide an effective user interfacefor cell phones, GPS devices, personal digital assistants (PDAs),computers, ATM machines, and other such devices.

Touchscreens use various technologies to sense touch from a finger orstylus, such as resistive, capacitive, infrared, and acoustic sensors.Resistive sensors rely on touch to cause two resistive elementsoverlaying the display to contact one another completing a resistivecircuit, while capacitive sensors rely on the capacitance of a fingerchanging the capacitance detected by an array of elements overlaying thedisplay device. Infrared and acoustic touchscreens similarly rely on afinger or stylus to interrupt infrared or acoustic waves across thescreen, indicating the presence and position of a touch.

Minimizing process steps to produce the touchscreen overlay andminimizing external wiring connections further reduce the cost ofproducing such a touchscreen display, and makes interfacing the displaywith electronic control circuitry more straightforward and reliable.Reducing wiring density and number also reduces the number of pinsrequired on a controller chip used to drive the electrode array, whichcan result in significant space and cost savings. Additionally, it isdesirable to reduce the layer count of the touchscreen assembly toreduce cost, reduce light absorption or other optical effects (inapplications where this is important), and to increase productionyields. Various methods have been proposed and implemented in priordesigns to simplify electrode wiring requirements, but often at theexpense of other design compromises such as reduced touch resolution oradded complexity or cost in other areas.

Capacitive and resistive touchscreens often use transparent conductorssuch as indium tin oxide (ITO) or transparent conductive polymers toform an array over the display image, so that the display image can beseen through the conductive elements used to sense touch. The size,shape, and pattern of circuitry have an effect on the accuracy of thetouchscreen, as well as on the visibility of the circuitry overlayingthe display. Although a single layer of most suitable conductiveelements is difficult to see when overlaying a display, multiple layerscan be easier to see, and circuitry patterns that align closely withpatterns on the display can form visible interference or moiré patterns.

Further, more complex patterns of touchscreen elements can require morecomplex routing of lines connecting the elements to external circuitryused to sense touch, such as external circuitry that drives varioustouchscreen elements and that detects capacitance between multipletouchscreen elements.

For these and other reasons, efficient and effective design oftouchscreen display elements is desired.

SUMMARY

A touchscreen assembly includes an array of pairs of electrode elementsdistributed across an active area of the touchscreen display assembly,such that the density of elements varies to create a sensing gradient.The position of an input on the touchscreen can be determined by theproportion of density of the pairs of elements in the area of the input.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a touchscreen assembly using a resistor network couplingtouchscreen elements, consistent with the prior art.

FIG. 2 shows first and second drive electrode arrays having electrodedensities that progressively vary in distribution proportion accordingto an example embodiment.

FIG. 3 illustrates electric fields emanating from electrodes in aself-capacitance touchscreen according to an example embodiment.

FIG. 4 shows a simple mutual capacitance touch sensing system accordingto an example embodiment.

FIG. 5 shows the simple mutual capacitance touch sensing system of FIG.4 with a finger present according to an example embodiment.

FIG. 6 illustrates a two-dimensional array of distribution modulatedtouchscreen electrodes according to an example embodiment.

FIG. 7 illustrates finger interaction with capacitive touchscreenelectrodes according to an example embodiment.

FIG. 8 illustrates an example touchscreen electrode sequence of fiveunique drive electrodes in groupings of five according to an exampleembodiment.

FIG. 9 illustrates an example touchscreen electrode sequence of fourunique drive electrodes in groupings of seven according to an exampleembodiment.

FIG. 10 illustrates first and second drive electrode arrays havingelectrode densities that vary in proportion progressively in thevertical direction according to an example embodiment.

FIG. 11 illustrates a three-connection receive electrode configurationfor a touchscreen display according to an example embodiment.

FIG. 12 illustrates a touchscreen display assembly comprising driveelements such as in FIG. 10 with receive elements such as in FIG. 11 sothat the elements do not overlap in the touchscreen active areaaccording to an example embodiment.

FIG. 13 shows a single layer touchscreen assembly overlaying a LCDdisplay panel according to an example embodiment.

FIG. 14 shows an exploded view of a dual layer touchscreen assemblyoverlaying a LCD display panel according to an example embodiment.

FIG. 15 shows the assembled dual layer touchscreen assembly of FIG. 14according to an example embodiment.

FIG. 16 shows a cellular telephone having a touchscreen displayaccording to an example embodiment.

DETAILED DESCRIPTION

Touchscreens include a wide variety of one-dimensional andtwo-dimensional geometries as may be used to form a slider, wheel,trackpad, tablet, or touchscreen, whether opaque, translucent ortransparent, and can be used with a finger, stylus, pen, or otheractuation method or device. The word ‘touchscreen’ will here be used toinclude any of the foregoing types of geometries or characteristics.

Capacitive touchscreens are able to detect a person's touch within anactive area, and report to a host device the location of one or moretouches with good accuracy and resolution. Some capacitive systems canalso detect the presence of objects other than a finger, such as astylus used to perform various functions.

Use of a touchscreen as part of a display also allows an electronicdevice to change the display image, presenting different buttons,images, or other regions that can be selected, manipulated, or actuatedby touch using one or more fingers. Touchscreens can therefore providean effective user interface for cell phones, GPS devices, personaldigital assistants (PDAs), personal computers and notebooks, ATMmachines, and other such devices.

Touchscreens use various technologies to sense touch from a finger orstylus, such as resistive, capacitive, infrared, and acoustic sensors.Resistive sensors rely on touch to cause two resistive elementsoverlaying the display to contact one another completing a resistivecircuit, while capacitive sensors rely on the capacitance of a fingerchanging the capacitance detected by an array of electrode elementsoverlaying the display device. Infrared and acoustic touchscreenssimilarly rely on a finger or stylus to interrupt infrared or acousticwaves across the screen, indicating the presence and position of atouch.

Capacitive and resistive touchscreens often use transparent conductorssuch as indium tin oxide (ITO) or transparent conductive polymers toform an array over the display image, so that the display image can beseen through the conductive elements used to sense touch. The size,shape, density, and pattern of circuitry have an effect on theresolution and accuracy of the touchscreen, as well as on the opticalcharacteristics of the electrode elements overlaying the display. Ingeneral it is desirable to have a high density of electrodes distributedalong both axes of the display, yet retain good optical properties suchas freedom from visible lines and patterns caused by the electrodesoptical properties. In some cases, optical properties are not important,for example in trackpads that do not overlay a display.

Although a single layer of most suitable conductive elements isdifficult to see when overlaying a display, multiple layers obstructmore light and can therefore be easier to see. While in many cases therequirements call for a high density of electrodes for better resolutionand accuracy, making the use of two or more layers unavoidable, there isa general desire to reduce the number of layers for optical reasons aswell as for cost reduction.

Further, more complex patterns of touchscreen electrodes, and largerscreen sizes, require more connecting lines to external circuitry; highconnection counts require more layers or finer geometries for therequisite denser spacing, thereby costing more money and creating yieldproblems in manufacture.

FIG. 1 shows a typical example of such a single-layer mutual capacitancetouchscreen display, consistent with the prior art. Here, thecapacitance between drive electrodes denoted with an “X” and variousreceive or sense electrodes designated with a “Y” is monitored, and achange in mutual capacitance between the electrodes indicates thepresence and position of an input such as a finger or other object. Inanother variation the Y electrodes are driven electrodes and the Xelectrodes are receive electrodes; the pattern is fully reversible,however throughout this patent the convention of X as drive and Y asreceive will be used to simplify discussion. Mutual capacitance sensorcircuitry measures the capacitance between the X electrodes and the Yelectrodes, which are covered by a dielectric overlay material thatprovides a sealed housing. When a finger is near the electrodes, fieldcoupling between the X and Y electrodes is attenuated, as the human bodyconducts away a portion of the field that arcs between the X and Yelectrodes, reducing the measured capacitive coupling between the X andY electrodes. This is illustrated in FIGS. 4 and 5, and discussed ingreater detail in the following description.

The X drive signals X1, X2, and X3 are here extended to varioustouchscreen drive elements using a resistor divider network chain ofresistors 101, linking the elements between the X or drive electrodesand resulting in electrical interpolation of signals from the electrodesacross the various X elements of the touchscreen. For example, the Xelement just below the X1 connection will receive a much stronger X1drive signal than an X2 drive signal, and the proportion of X1 and X2drive signal strengths that couple with the Y electrodes will indicatethe relative vertical position of a finger on the display assemblyshown. Similarly, a finger placed in the lower half of the displayassembly of FIG. 1 will impact capacitive coupling between one of the Xelectrodes having some proportion of X2 and X3 drive signals, where theproportion indicates which X element is nearest the finger.

The X drive electrodes are driven using different series of pulses inone embodiment, such that a suitable number of pulses create an electricfield that capacitively couples to the receiving Y electrode. The numberof pulses needed is dependent on the geometry of the touchscreenelectrodes, the dielectric front panel overlaying the electrodes, andother such performance and design characteristics. If each X driveelectrode uses a different series of pulses, or is pulsed at differenttimes, the presence and vertical position of a finger can be determinedby observing which X drive signals have their capacitive coupling to theY elements attenuated, and in what proportion the signals areattenuated.

The Y elements of FIG. 1 are similarly split into three regions and havea tapered geometry, such that a finger's presence on the far left sideof the touchscreen will affect capacitive coupling between X electrodesand a Y1 sense electrode, a touch near the center of the touchscreenwill affect capacitive coupling between X electrodes and a Y2 senseelectrode, and a touch near the right side of the touchscreen willaffect capacitive coupling between X electrodes and a Y3 senseelectrode. Touches somewhere between the center and sides of thetouchscreen will affect capacitive coupling in proportion to the area ofthe tapered Y electrodes under the finger, making horizontal estimationof the finger's position determinable by evaluating the proportion ofY1, Y2, and Y3 capacitive coupling that is disrupted due to the finger'spresence.

The touchscreen of FIG. 1 relies on the presence of resistors 101 tointerpolate the X drive signals between the various X elements of thetouchscreen, requiring not only that various conductive traces be laiddown to form the touchscreen, but that the X element conductive tracesalso be electrically coupled to a network of resistors or resistivematerial having resistances that are reasonably well controlled as tomatching tolerance. This adds extra steps, and considerable cost andcomplexity to the production process, additionally it also compromisesthe performance of the sensing circuit, since the resistors introduce anelevated RC time-constant which requires more time to charge anddischarge fully, thereby slowing down the acquisition process andpotentially introducing other side effects such as increased noisesusceptibility. While this design does in fact reduce wiring countthereby reducing space and some cost aspects, it introduces new problemsand increases costs in other aspects.

One example touchscreen embodiment therefore uses capacitive touchscreenelements in progressively varying electrode densities or proportionsacross at least one dimension to provide varying field or senseproportional intensities across the touchscreen display.

FIG. 2 shows in plan view a linear capacitive touch slider 201, whereintwo self-capacitance electrode sets A and B are configured with varyingdistributions along the long axis to effect a sensing gradient which canbe interpreted by suitable capacitance sensing circuitry to report thecentroid of finger touch 202 (in outline) along the long axis.

Notably the distribution of A and B electrodes can be convenientlyorganized into subgroups or zones, each zone having a varying ratio of Aversus B electrode types. For example at the top of the slider in Zone1, the ratio is 5:0 of A:B, i.e., there are five A electrodes in thisspace versus zero B electrodes. In Zone 2, the ratio is 4:1, and so onuntil zone 6 is reached where the ratio is 0:5. This modulation ofelectrode density, and appropriate placement of electrode types withineach zone, facilitates a smooth, linear gradient for the purposes oftouch reporting as will be seen.

FIG. 3 shows the fields emanating from electrodes A of FIG. 2 in crosssection along the area of touch 202 (but with no finger present). Inself-capacitance systems, the electric fields 301 propagate outwardsfrom the electrodes 302 in all directions; only field lines propagatinginto the panel are shown diagrammatically for clarity in FIG. 3. Thefields propagating through panel 303 are those that can interact with atouch on the upper surface of 303; increases in field strength, i.e.increases in capacitance, result from touch in inverse proportion to thedistance and proportional to the surface area of the finger, and whichcan be approximated according to the standard formula Ct=εA/d, where:

-   -   Ct=the increase in capacitance for one sensing channel due to        touch,    -   ε=relative permittivity of the panel material,    -   A=The intersecting surface area of the electrodes coupled to the        sensing channel affected and the finger contact area,    -   d=thickness of the dielectric panel

The value Ct is only approximation, since the above formula does notinclude effects from fringe fields, human skin thickness and moisturecontent, human body to sensor return path coupling, and the like.Substantial variability in Ct may be observed over a broad range ofparametric conditions, nevertheless the formula nevertheless representsa good first order approximation.

Sensing circuitry 304 has two channels, A and B, to drive the respectiveelectrodes 302. The capacitive sensing circuitry 304 can be of any styleknown or unknown to the art, and is not important in understanding theinvention.

FIG. 4 shows the field lines associated with electrodes with mutualcapacitive coupling. Here, field lines from a driven electrode 401(shown as X) operated by a driver 402 and a receive electrode 403 (shownas Y) coupled to a receiver 404, the fields penetrating through panel405. A portion of the emitted field 406 escapes into free space or otherparts of the panel as shown, however we are here primarily concernedwith the part of the field which arcs from the X electrode to the Yelectrode.

FIG. 5 shows the electrode configuration and circuit of FIG. 4 where thepanel is touched by a finger. Here, the finger 501 causes field lines502 normally coupling from drive electrode 503 to receive electrode 504as shown at 506 to be absorbed by the finger 501. The result of thisaction is a very detectable decrease in signal level by receiver 505.

FIG. 6 shows a 2-dimensional sensor array such as a touchscreen, whereinelectrodes are arrayed along both the horizontal and vertical axes in afashion similar to what is shown in FIG. 2. The touchscreen shown at 600can be extended by adding more drive and receive channels, and the sizeof the panel is not limited to what is shown here. Crossovers 601facilitate wiring along the periphery of the active area. A touch 602creates signal changes on the XA, XB, YA, and YB electrodes so as toprovide sufficient information to signal sensing and processingcircuitry to locate the centroid of touch with good accuracy along bothaxes. In self capacitance mode, the electrodes XA and XB operateidentically to YA and YB but are rotated, and use the same circuitry forexample of type 304 of FIG. 3. The main sensing area of 600 as shownemploys two sensing layers, one for X and one for Y electrode sets, or,employs a single layer with crossovers at each intersection of an X anda Y electrode.

The electrode array of FIG. 6 can also be operated in mutual capacitancemode, similar to that described in conjunction with FIG. 1. In thismode, the electrodes along one axis, for example those controlled by XAand XB, are driven to cause fields to be emitted into a panel such as303 of FIG. 3. The other electrode array, for example YA plus YB,receive the electric fields from XA and XB; signals from YA and YB areacquired and processed to provide a location of touch along both thehorizontal and vertical axis.

FIG. 7 shows use of intrinsic interpolation to achieve a smooth positionresponse using self-capacitance. It should be understood that mutualcapacitance uses similar principles, but the field lines arise from andare affected by slightly different principles. Here, electrodes 701 emitfields into space through the dielectric panel 702 including to a finger703, the changes in strength of which can be modeled as a set ofdiscrete ‘disturbance capacitances’. The value of each disturbancecapacitance is dependent on the degree of proximity of the finger 703 toeach electrode in accordance with the discussion of FIG. 3.

Because each such capacitance 704 can be of any intermediate value, thedisplacement of touch location can be modeled as an interpolationproblem where the point-by-point values are added and a ratio takenbetween the affected sensing channels. In the example shown, the weightsof all A and B electrodes are separately summed intrinsically in thesensing process to arrive at two numbers, from which a ratiometricposition can be derived. Since all A electrodes are connected togetherto one sensing channel, and all B electrodes are connected together to asecond sensing channel, the detection circuitry has no need to know theindividual signal deltas for each A or B sub-electrode in order todetermine location of touch.

Furthermore, it should be clear that the ‘core’ area of touch,comprising the values from 15.8 to 17.2 in the example shown in FIG. 7,is not the sole determinant of signal strength; in fact, the fringefields between the electrodes and the finger when an airgap exists arealso important in locating touch, as these weaker signals contributestrongly in aggregate to the interpolative process, creating a smooth,non-granular positional response relative to the underlying granularityin electrode frequency and distribution. These fringe fields exhibit alargely Gaussian rolloff response in two dimensions, i.e., around theperimeter of the finger touch area, and exist in both self and mutualcapacitance operating modes.

If mutual capacitance is employed the electrodes will exist assend/receive pairs and the signal levels will drop with increasingobject proximity, however the interpolative principles are identical tothat of self-capacitance including as to fringe-field effects, varyingonly in matter of degree. It should be understood that the positionformula shown at 705 is only an example used for illustration and is notthe only possible method to calculate position. In a 2D sensor array,the equations used to locate position can become quite sophisticated;the formula for computation is not critical, and discussion of theexamples presented here do not limit the scope of the invention orclaims.

FIGS. 4 and 5 are important to understanding the operation of theinterpolative process described in association with FIG. 7, if FIG. 7 isoperated using electrode pairs in a mutual capacitance mode rather thana self-capacitance mode as drawn. As mentioned previously, in a mutualcapacitance implementation the electrodes of FIG. 7 would be replacedwith alternating drive and receive electrodes from which the fieldswould arise.

FIG. 8 shows a group sequence of electrode wiring. The wiring sequenceillustrated here can apply equally to self and mutual capacitance. FIG.8 also shows that more than two electrode types can be used along eachaxis, for example in this example there are five channels of sensing,A-E. While FIG. 8 uses five groupings of five channels, otherarrangements are possible, for example as shown in FIG. 9, which showsseven groupings of four channels. Arrangements can include any arbitrarynumber of elements per group and groups per screen axis, according tothe needs of a particular design, however a reasonable group size mighttypically include at least 3 elements per group. It can also beunderstood from FIG. 8, that the plan layout of FIGS. 2 and 6 comprisebut one zone of FIG. 8, for example from zone A1 to zone B1. Extensionsin length can therefore be accommodated by means of added sensingchannels, for example, channels C through E as shown in FIG. 8, withoutlimit.

FIG. 10 shows in plan view an electrode layer comprising two channels ofmutual or self capacitance, XA and XB, arranged with a vertical split inthe middle. Connections for XA and XB exist on the left and right sides,and it should be understood that XA on the left side is the sameconnection as XA on the right side, and similar for XB. This pattern issimilar to FIG. 2 with the exception of the split arrangement as shownat 1003. This electrode layer 1001 on its own, can only resolve positionalong the vertical axis as drawn.

In a further example, two drive signals XA and XB drive two separate butinterleaved arrays of horizontal X drive electrodes, as shown generallyat 1001. When a finger touches the touchscreen such as at location 1002,the finger desirably interacts with several X drive electrodes,overlaying the XA and XB drive electrodes in proportion to the finger'sposition on the touchscreen. In this example, the electrodes coupled tothe XA drive signal are in higher proportion near the top of thetouchscreen, such that a person who touches the touchscreen in region1002 intersects with approximately six or seven XA drive electrodes andonly one XB drive electrode. The relative proportion of XA electrodeintersected to XB electrode intersected suggests here that the finger isapproximately one sixth XB and five sixths XA, or one sixth of the waydown from the top of the touchscreen display.

Fine grain position information comes from intrinsic interpolationincluding from fringe fields as discussed in conjunction with FIG. 7.The electrode spacing and group extent along the vertical axis aretypically optimized for smooth performance, for example by making thegroup extent no more than comparable in dimension to a longitudinalfingerprint chord. The vertical extent of the panel 1001 can beincreased by the use of additional X drive electrodes, for example usingan extended and/or enlarged sequence as shown in FIGS. 8 and 9.

In further embodiments, the drive electrodes of FIG. 10 are made ofvarious materials such as indium tin oxide, conductive polymer, metalwire, or fine line metal. A more detailed example includes fine linemetal electrodes that are approximately 10 micrometers in width or less,and occupy less than 10% of the total screen area, and in a furtherexample less than 5%.

As discussed previously, the arrangement of FIG. 10 resolves positiononly along the vertical axis; the horizontal axis is provided by theplan layout of FIG. 11, which is interleaved with that of FIG. 10 tocompose a single-layer layout shown in FIG. 12. The purpose of gap 1003of FIG. 10 is to allow the spine 1103 of FIG. 11 to fit down the middleas shown in FIG. 12, to provide for three sensing channels along thehorizontal axis.

In FIG. 11, three different receive electrodes Y0, Y1, and Y2 arecoupled to the control circuitry, and the three electrodes are coupledto Y elements that are configured in an alternating pattern as showngenerally at 1101 such that a the location of a finger touch 1102 coversvarying proportions of different Y receive electrodes as it moves fromside to side across the touchscreen display. For example, a touch inposition 1102, covering mostly region 4 but also overlapping regions 3and 5, covers somewhat more Y2 element electrodes than Y1 elementelectrodes. This indicates that the finger is slightly to the right ofthe center of region 4, toward the Y2 receive element side of theregion.

The Y receive electrodes are therefore able to use interpolation of thefinger's impact on capacitive coupling to determine the finger'sposition with greater accuracy than the five zones laid out in FIG. 11,much as interpolation or proportional measurements were used in FIG. 10to determine the finger's position in the vertical axis using X driveelectrodes. A relatively straightforward array of X drive electrodes asin FIG. 10 and Y receive electrodes as in FIG. 11 can therefore becombined to provide a high-performance touchscreen display with verygood finger resolution capability along both axes, as is shown in FIG.12.

The composite design of FIG. 12 therefore resides in one plane, exceptfor crossovers 1203 on the periphery of the active area. The Y electrodelayer shown in FIG. 11 uses alignment and length-modulation to achievebetter interpolation; distribution modulation exists only on layer 10,as it is difficult to fashion 2-axis distribution modulation in a singlelayer. However, the design of FIG. 12 eliminates the need for resistors101 of FIG. 1, yet provides similar resolution and accuracy in a singlelayer to the design of FIG. 1, even with one less X channel.Distribution modulation does not suffer from RC time constant problemsintroduced by the divider resistors of FIG. 1, thereby allowing for agreater extent of each drive channel than the resistive dividerapproach, resulting in fewer required drive channels over a given lengthof screen area.

Looking generally at the touchscreen display region 1201, the Y receivegrid of FIG. 11 is laid in between the X drive electrodes of FIG. 10,such that the X drive electrodes and Y receive electrodes do not overlapin the display region. This enables formation of the entire electrodeset on a substrate using a single process, such as by single pass metalor ITO deposition, resulting in a relatively efficient and inexpensiveproduction process. Further, as electrodes do not cross within thedisplay region, there are no regions of the touchscreen display that aremore opaque than others, as there are no “stacked” or overlappingelectrodes. The distribution of electrodes across the touchscreendisplay is also generally uniform, resulting in relatively uniformbrightness across the touchscreen display.

In operation as a mutual capacitance touchscreen, a user of touchscreendisplay 1201 places a finger on or near the touchscreen, as shown at1202. Different series of pulses are sent via the Xa and Xb driveelectrodes, such that the mutual capacitance between the different Xdrive electrodes and Y conductors can be separately determined, such asby observation of an RC time constant, received pulse amplitudemeasurement, charge transfer measurement, or another suitable method.When the presence of a finger interrupts the field between the X and Yconductors as in FIG. 5, a reduction in observed coupling between thedrive and receive electrodes is observed.

As noted previously, many designs such as that of FIG. 12 can operate ineither self or mutual capacitance modes, and in mutual capacitance modeeither the X or the Y electrodes can be the driven electrodes.

The touchscreen display of FIG. 12 has several advantages relative tothat of FIG. 1, including the lack of a resistive material coupling theX drive electrodes to interpolate X drive signals between the X driveelectrodes. Fewer different materials and process steps are thereforeneeded to form the touchscreen display of FIG. 12, and a reducedconnection count simplifies connection to external drive and controlcircuitry.

FIG. 13 shows one physical implementation of a single electrode layerstack over a display such as an LCD. The electrodes 1301 are printed orotherwise fashioned onto a substrate 1302, which in some embodiments isa clear plastic sheet such as PET or polycarbonate, or potentially aglass layer. Adhesive 1303 is used to bond substrate layer 1302 to panel1304; 1303 may be a liquid adhesive, or an adhesive sheet. Assembly maybe via a laminating process to provide for an airtight assembly.Electrodes 1301 may be fashioned from clear ITO, or from ultra fine linemetal traces when used with a display. If no display is used, then theoptical properties of assembly 1305 are not relevant and any set ofsuitable materials may be used. Gap 1306 is an airgap between thedisplay and the assembly 1305, as is common in the art. In some cases isit advantageous to insert an adhesive layer in this gap and laminate theentire stack to the top of the display.

FIG. 14 shows an assembly stack 1401 which contains two sensing layers,for example as may be used to implement a two-layer version of thedesign of FIG. 6. Two layers of plastic film are used, 1402 and 1403,with respective electrodes 1404 and 1405 fashioned thereon, andassembled with adhesive layers 1406, 1407 and optionally 1408 via alamination process to panel 1409 and possibly also to display 1410.

FIG. 15 shows the layer stack of FIG. 14 as laminated together, butwithout the adhesive layer 1408, using instead an airgap 1501.

Touchscreens are often used in a variety of applications, from automaticteller machines (ATM machines), home appliances, personal digitalassistants and cell phones, and other such devices. One such examplecellular telephone or PDA device is illustrated in FIG. 16. Here, thecellular telephone device 1601 includes a touchscreen display 1602comprising a significant portion of the largest surface of the device.The large size of the touchscreen 1602 enables the touchscreen topresent a wide variety of images that can serve along with touchscreencapability to provide input to the device, including a keyboard, anumeric keypad, program or application icons, and various otherinterfaces as desired.

The user may interact with the device by touching with a single finger,such as to select a program for execution or to type a letter on akeyboard displayed on the touchscreen display assembly 1602, or may usemultiple touches such as to zoom in or zoom out when viewing a documentor image. In other devices, such as home appliances, the display doesnot change or changes only slightly during device operation, and mayrecognize only single touches.

Although the example touchscreen display of FIG. 16 is configured as arectangular grid, other touch sensitive device configurations arepossible and are within the scope of the invention, such as atouchwheel, a linear slider, buttons with reconfigurable displays, andother such configurations. Proportionate distribution of drive orreceive electrodes coupled to different elements across the touchsensitive device can be adapted to any such shape, enabling detection ofthe region of input on the touchscreen.

In many embodiments, it is desirable that the conductive material beeither transparent, such as Indium tin oxide or transparent conductivepolymer, or be so small as to not significantly interfere withvisibility of the display, such as with fine line metal.

Although the proportional element distribution touchscreen displayassembly examples given here generally rely on mutual capacitance orself-capacitance to operate, other embodiments of the invention will useother technologies, including other capacitance measures, resistance, orother such sense technologies.

These example touchscreen assemblies illustrate how a touchscreen can beformed using an array of drive electrodes having a distributionmodulation that enables determining an input position by the sensinggradient observed. The drive electrodes in a further example do notoverlap in the active area or field of the touchscreen, eliminating theextra materials, expense, and production steps needed to formresistively-coupled element touchscreens such as that of FIG. 1. By notoverlapping electrodes in the usable field, image quality is notdegraded, and the relatively uniform electrode density of all electrodesacross the touchscreen element avoids causing bright or dark regions inareas of varying electrode density when viewing the display through thetouchscreen element.

Configurations such as the example of FIG. 12 provide an efficientsystem for generating an accurate reading of a finger's location on thetouchscreen assembly. These benefits simplify operation of thetouchscreen panel, as fewer connections and less filtering and otherdata processing are needed to ensure reliable touchscreen operation.This in turn leads to lower power consumption in an electronic deviceincorporating such a touchscreen display assembly, improving powerefficiency, increasing battery life, and reducing resource use such asmemory and processor consumption.

The invention claimed is:
 1. An assembly comprising: an array of firstelectrodes distributed across an active area of a touchscreen assemblysuch that the density of first electrodes increases in a first directionalong an x-axis of the touchscreen, wherein the first electrodes arecoupled together in a first sensing channel; an array of secondelectrodes distributed across an active area of the touchscreen assemblysuch that the density of second electrodes decreases in the firstdirection along the x-axis of the touchscreen, wherein the secondelectrodes are coupled together to in a second sensing channel; an arrayof third electrodes distributed across an active area of a touchscreenassembly such that the density of third electrodes increases in a seconddirection along a y-axis of the touchscreen; and an array of fourthelectrodes distributed across an active area of the touchscreen assemblysuch that the density of fourth electrodes decreases in the seconddirection along the y-axis of the touchscreen.
 2. The assembly of claim1, wherein: the first electrodes are directly coupled to one another andto a first external electrical connection; and the second electrodes aredirectly coupled to one another and to a second external electricalconnection.
 3. The assembly of claim 1, wherein the density of first andsecond electrodes changes by varying the proportion of first and secondelectrodes present across the first direction.
 4. The assembly of claim1, further comprising an array of fifth electrodes distributedapproximately evenly across the touchscreen, wherein: the first andsecond electrodes are drive electrodes, and the fifth electrodes arereceive electrodes such that the first and second electrodes interactwith the fifth electrodes via mutual capacitance to form a mutualcapacitance touchscreen.
 5. The assembly of claim 1, wherein at leastone of the first and second electrodes comprise at least one of metalwire, fine line metal, indium tin oxide, and a conductive polymer. 6.The assembly of claim 1, wherein the first and second electrodes arenonintersecting in the active area of the touchscreen.
 7. The assemblyof claim 1, wherein the touchscreen assembly comprises at least one of aself-capacitance touchscreen, a mutual capacitance touchscreen, and aresistive touchscreen.
 8. A method comprising: driving an array of firstelectrodes with a first drive signal, the first electrodes distributedacross an active area of a touchscreen assembly such that the density offirst electrodes increases in a first direction along the x-axis of thetouchscreen, wherein the first electrodes are coupled together in afirst sensing channel; driving an array of second electrodes with asecond drive signal, the second electrodes distributed across an activearea of the touchscreen assembly such that the density of secondelectrodes decreases in the first direction along the x-axis of thetouchscreen, wherein the second electrodes are coupled together in asecond sensing channel; driving an array of third electrodes with athird drive signal, the third electrodes distributed across an activearea of a touchscreen assembly such that the density of third electrodesincreases in a second direction along a y-axis of the touchscreen; anddriving an array of fourth electrodes with a fourth drive signal, thefourth electrodes distributed across an active area of the touchscreenassembly such that the density of fourth electrodes decreases in thesecond direction along the y-axis of the touchscreen.
 9. The method ofclaim 8, wherein: the first electrodes are directly coupled to oneanother and to the first drive signal, and the second electrodes aredirectly coupled to one another and to the second drive signal.
 10. Themethod of claim 8, wherein the density of first and second electrodeschanges by varying the proportion of first and second electrodes presentin the first direction.
 11. The method of claim 8 further comprising:receiving a mutual capacitive coupled signal from at least one of thefirst and second electrodes in an array of fifth electrodes distributedapproximately evenly across the touchscreen, such that the first andsecond electrodes interact with the fifth electrodes via mutualcapacitance to form a mutual capacitance touchscreen.
 12. The method ofclaim 11, wherein the first, second, and fifth electrodes arenonintersecting in the active area of the touchscreen.
 13. A methodcomprising: forming an array of first electrodes distributed across anactive area of a touchscreen assembly such that the density of firstelectrodes increases in a first direction along an x-axis of thetouchscreen; coupling the first electrodes together in a first sensingchannel; forming an array of second electrodes distributed across anactive area of the touchscreen assembly such that the density of secondelectrodes decreases in the first direction along the x-axis of thetouchscreen; coupling the second electrodes together to in a secondsensing channel; forming an array of third electrodes distributed acrossan active area of a touchscreen assembly such that the density of thirdelectrodes increases in a second direction along a y-axis of thetouchscreen; and forming an array of fourth electrodes distributedacross an active area of the touchscreen assembly such that the densityof fourth electrodes decreases in the second direction along the y-axisof the touchscreen.
 14. The method of claim 13, further comprising:directly coupling the first electrodes to one another and to a firstexternal electrical connection; and directly coupling the secondelectrodes to one another and to a second external electricalconnection.
 15. The method of claim 13, wherein the density of first andsecond electrodes is changed by varying the proportion of first andsecond electrodes formed across the first direction.
 16. The method ofclaim 13, further comprising forming an array of fifth electrodesdistributed approximately evenly across the touchscreen, such that thefirst and second electrodes interact with the fifth electrodes viamutual capacitance to form a mutual capacitance touchscreen display. 17.The method of claim 16, wherein at least one of the first, second, andfifth electrodes comprise at least one of fine line metal, indium tinoxide, and a conductive polymer.
 18. The method of claim 16, wherein thefirst, second, and fifth electrodes are nonintersecting in the activearea of the touchscreen.
 19. An assembly comprising: an array of firstelectrodes distributed across a plurality of zones of an active area ofa touchscreen assembly; and an array of second electrodes distributedacross the plurality of zones of the active area of the touchscreenassembly; and an array of third electrodes distributed across theplurality of zones of the active area of the touchscreen assembly; andan array of fourth electrodes distributed across the plurality of zonesof the active area of the touchscreen assembly, and wherein: the firstelectrodes are coupled together in a first sensing channel; the secondelectrodes are coupled together in a second sensing channel; in a firstzone disposed along an x-axis of the touchscreen assembly, there are agreater number of first electrodes than second electrodes, and in asecond zone disposed along the x-axis of the touchscreen assembly, thereare a fewer number of first electrodes than second electrodes; in afirst zone disposed along a y-axis of the touchscreen assembly, thereare a greater number of third electrodes than fourth electrodes, and ina second zone disposed along the y-axis of the touchscreen assembly,there are a fewer number of third electrodes than fourth electrodes. 20.The assembly of claim 19, wherein a position of an input on thetouchscreen assembly can be determined by the proportion of first andsecond electrodes in the area of input.
 21. The assembly of claim 19,wherein: a third zone is disposed between the first zone and the secondzone along the x-axis of the touchscreen assembly, there are a fewernumber of first electrodes in the third zone than a number of firstelectrodes in the first zone, and there are a greater number of secondelectrodes in the third zone than a number of second electrodes in thesecond zone.